This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/JP00/01130 which has an International filing date of Feb. 25, 2000, which designated the United States of America and was not published in English.
This invention relates to an exhaust gas recirculation (referred to as EGR, hereinafter) valve controller provided in an exhaust gas recirculation system.
FIG. 1 is a constitutional view of an engine exhaust system, in which the control valve 11 of an EGR valve is arranged in an exhaust recirculation passage c for communicating the exhaust passage a and the intake passage b of an engine E with each other. This EGR valve controller is adapted to control the opening/closing of the control valve 11 by, for example, a stepping motor M of a hybrid PM 4-phase type or the like. The EGR valve controller controls the.opening angle of the control valve 11 by subjecting.the stepping motor M to open loop control in steps of a stepping angle.
The controller using such a stepping motor M is capable of controlling the opening angle of the control valve 11 only in steps of the stepping angle of the stepping motor M. Thus, there is a limit to the resolving power of the control valve 11 to control the opening angle. In addition, in the open control of the stepping motor M, a power swing phenomenon sometimes occurs, placing a limit on responsiveness. Once power swing occurs, a difference occurs in controlled variables, and this difference is maintained, consequently reducing reliability.
EGR valve controllers designed to deal with the foregoing problem have been available in the related art. For example, Japanese Patent Laid-Open Application Hei 10 (1998)-122059 discloses a controller for an EGR valve, which opens/closes on a torque balance between a predetermined return torque applied in the opening/closing direction of the control valve 11 by pressing means, and a variable motor torque applied in the closing/opening direction of the control valve 11 by the energization of a direct current motor (referred to as a DC motor, hereinafter) in one direction. This controller comprises: an open loop control system for open-loop controlling the DC motor in such a way as to generate a motor torque corresponding to the target opening/closing position of the control valve 11; and a feedback control system for feedback-controlling the DC motor based on deviation between input data indicative of the target opening/closing position of the control system 11, and detection data indicative of the actual opening/closing position of the control valve 11.
First, a driving system using the above DC motor will be described. To feedback-control the opening angle of the control valve by a DC servo motor system, the opening angle of the control valve 11 is continuously detected and fed back by using a position sensor of a sliding resistance type or the like. Thus, by continuously controlling the torque generated by the DC motor, the resolving power of the control valve 11 to control an opening angle can be infinitely reduced theoretically. In the DC motor, unlike the case of the stepping motor M, there are no control errors caused by a power swing phenomenon. Accordingly, responsiveness can be improved compared with a case in which the stepping motor M is used, thus enhancing reliability.
The EGR valve driving system using such a DC motor employs a so-called torque balance system, which is adapted to control valve opening/closing on a torque balance between a predetermined return torque applied in a closing direction (or opening direction) by a spring as pressing means, and a variable motor torque applied in an opening direction (or closing direction) by the energization of the DC motor in one direction. In the case of such a driving system, since the return torque is always applied to the EGR valve, the inclinations of lines A and B undergoing a hysteresis caused by friction exhibits a difference, as shown in FIG. 2.
Referring to FIG. 2, the line A indicates an operation characteristic when the control valve 11 is opened by increasing the motor torque; and the line B an operation characteristic when the control valve 11 is closed by reducing the motor torque. The inclinations of the lines A and B are changed by a spring constant of the spring applying the return torque, and the lines A and B are shifted left and right in FIG. 2 according to the magnitude of a set torque.
It is now assumed that the mere PI control is employed to control the control valve 11 of the foregoing operation characteristics, wherein the DC motor is subject to proportion and integration (PI) control based on a deviation between input data indicative of the target opening/closing position of the control valve 11, and detection data indicative of the actual opening/closing position of the same. In this case, because of the operation characteristics shown in FIG. 2, it is difficult to maintain the control valve 11 in the target opening/closing position.
Specifically, proportion (P) and integration (I) gains must be increased in order to execute control along the line A, considering the operation characteristics shown in FIG. 2. However, under such setting, when the motor torque is increased based on the PI control, the deviation from the target opening position becomes xe2x80x9c0xe2x80x9d immediately after the control valve 11 is opened to the target opening position, setting a P component equal to xe2x80x9c0xe2x80x9d and clearing an I component, and the closing of the control valve 11 is immediately started by the return torque. In an initial stage when the valve closing has just started (small deviation), the motor torque cannot overcome the return torque because the P and I components are both small, thus enlarging deviation. Thereafter, even if the deviation grows to a point that the motor torque and the return torque are balanced, the closing operation of the control valve 11 cannot be stopped suddenly due to the inertia of the DC motor, and consequently the opening operation of the control valve 11 cannot be immediately started. If a gain is increased in such a way as to generate relatively large motor torque even when the deviation is small, as shown in FIG. 3, the process is brought into a vicious cycle of increased overshoots and undershoots.
A description will be given of one related-art construction of the controller of the control valve based on a so-called torque balance driving system using the DC motor, by referring to FIGS. 4 to 7. In FIG. 4, a reference numeral 1 denotes a valve body having an exhaust recirculation passage c formed in the recirculation system of exhaust gas. The control valve 11 is raised as shown to be brought into contact with a seat 12, thereby closing the exhaust passage c. The control valve 11 is lowered to be separated from the seat 12, thereby opening the exhaust passage c.
A reference numeral 2 denotes a motor case for housing a DC motor 20. This DC motor 20 includes a rotor 21 having a coil 22 wound thereon, and a yoke 23 having a magnet 24. The upper end part of the rotor 21 is rotatably supported in the motor case 2 by a slide ball 25 and a rotor shaft 26. The lower end part of the rotor 21 is rotatably supported in the valve body 1 by a bearing 27. A commutator 28 is attached to the upper end of the rotor 21, and the motor brush 30 of the motor case 2 side is pressed against the commutator 28 by a brush spring 29.
A reference numeral 40 denotes a position sensor for detecting the rotational position of the rotor 21, a resistance value of the position sensor 40 varying according to the rotational position of the rotor 21. The position sensor 40 and the motor brush 30 are connected to the controller (described later) by a connector terminal 3.
A motor shaft 31 is engaged inside the rotor 21, and the motor shaft 31 is prevented from being rotated by the guide bush 13 of the body 1. Accordingly, the motor shaft 31 is raised and lowered in proportion to the magnitude of rotation of the rotor 21. A shaft 14 is abutted against the lower end of the motor shaft 31. The middle part of the shaft 14 is guided so as to be freely raised and lowered in the valve body 1 by a guide seal 15 and a guide plate 16. The control valve 11 is attached to the lower end of the shaft 14.
A reference numeral 17 denotes a guide seal cover. Between a spring seat 18 attached to the upper end of the motor shaft 14, and the guide plate 16, a spring 19 is provided to press the shaft 14 upward, i.e., in the closing direction of the control valve 11.
The control valve 11 constructed in the foregoing manner is driven by a torque balance system like the one described above. Specifically, the EGR valve is designed such that the control valve 11 is controlled to be opened/closed based on a torque balance between a predetermined return torque applied in the closing direction of the control valve 11 by the spring 19 as pressing means, and a variable motor torque applied in the opening direction of the control valve 11 by the energization of the DC motor 20 in one direction.
FIG. 5 is a constitutional view schematically showing the entire controller, in which a motor driving voltage is determined by a control unit 50 implemented by a microcomputer. A reference numeral 52 denotes a battery; and 53 a motor driving voltage conversion unit for converting the output of a PI controlled variable operation unit 63 (described later), and feeding the converted result to the DC motor 20. The operation unit 63 includes a Zener diode 53a, a diode 53b for controlling a current to flow in one direction in the DC motor 20, a field-effect transistor (FET) 53c, and an interface provided between the control unit 50 and the FET 53c. A reference numeral 56 denotes a regulator for securing a driving voltage (5V) for the control unit 50.
The control unit 50 receives a detected signal from a running state quantity sensor 57 such as a crank angle sensor or the like, and a detected signal from the position sensor 40 supplied via interfaces 58 and 59, respectively. The position sensor 40 of the described example has a movable contact part 42 moved on a resistor 41, to which a constant voltage (5V) is applied from a voltage supply unit 60. This movable contact part 42 is moved in accordance with the rotation of the rotor 21 and, accordingly, a voltage corresponding to the rotational position of the rotor 21 is outputted as a detected signal from the movable contact part 42.
In addition, the motor driving voltage conversion unit 53 is adapted to control an average driving voltage applied to the DC motor 20, by turning ON/OFF a voltage applied to the DC motor 20 at a fixed cycle, and switchably operating the FET 53c based on a PWM signal corresponding to a ratio of ON time to OFF time (driving duty) per cycle.
FIG. 6 is a block diagram schematically showing a control system composed of the control unit 50. In FIG. 6, a reference numeral 61 denotes a target position operation unit for obtaining an optimal opening/closing position of the control valve 11 based on the detected signal of the running state quantity sensor 57. The target position operation unit 61 outputs a voltage (referred to as a xe2x80x9ctarget value (1)xe2x80x9d, hereinafter) corresponding to the target position 62 denotes an A/D conversion unit for subjecting the detected signal of the position sensor 40 to A/D conversion. The A/D conversion unit 62 outputs a voltage (referred to as a xe2x80x9ccurrent value (2)xe2x80x9d, hereinafter) corresponding to the current opening/closing position of the control valve 11. 71 denotes an adder/subtractor adding or subtracting one from the other the target and current values (1) and (2). Based on a deviation between the target and current values (1) and (2), the PI controlled variable operation unit 63 calculates a PI controlled variable (voltage) composed of a proportion component (P component) and an integration component (I component), and then outputs the variable.
FIG. 7 is a detailed view of the PI controlled variable operation unit 63. Reference numerals 72 and 73 denote amplifiers for amplifying the output of the adder/subtractor 71; 74 an integrator for integrating the output of the amplifier 73; 75 a subtractor for subtracting one from the other the outputs of the amplifier 72 and the integrator 74; 76 an amplifier having a saturation function for saturating the output of the subtractor 75; and 77 a display for displaying the target and current values (1) and (2), and the output value of the amplifier 76.
FIG. 8(a) is a graph showing the variation of the detection value (ordinate) of the position sensor 40 with respect to time (abscissa), in which indicates an ideal characteristic, and L an actual operation characteristic. FIG. 8(b) is a graph showing the variation of the applied voltage of the DC motor with respect to time (abscissa).
Next, an operation will be described.
As shown in FIG. 7, the feedback control system performs PI control to compensate for a deviation (excess/shortage of open loop control) between the current and target values (2) and (1). As a result, the control valve can be stabilized at the target position irrespective of the opening/closing direction of the control valve 11.
In the related-art PI controlled variable operation unit 63 shown in FIG. 7, when a feedback quantity is increased, a voltage applied to the DC motor 20 varies with time as shown in FIG. 8(b), concurrent with the variation of the detection quantity (FIG. 8(a)) of the position sensor 40 for detecting the control valve position. Due to hysteresis as shown in FIG. 15(a), which is a graph showing the variation of a characteristic of a valve opening angle with respect to a motor driving voltage value, the control is delayed by a hysteresis amount W. As a result, the control valve position exhibits xe2x80x9chuntingxe2x80x9d around a target position. It remains necessary, however, that a feedback quantity must be sufficiently increased to operate the valve mechanism at a response speed for which the valve mechanism is made for.
In the conventional exhaust gas recirculation valve controller constructed in the foregoing manner, because of hysteresis, responsiveness is low, and it is impossible to accurately control the control valve.
The present invention is designed to solve the foregoing problems, and it is an object of the invention to provide an exhaust gas recirculation valve controller capable of canceling hysteresis, and improving controllability based on the input quantity of the PI controlled variable operation unit or an operation quantity outputted from the PI controlled variable operation unit.
In accordance with the present invention, there is provided a controller for an exhaust gas recirculation valve adapted to open/close on torque balance between a return torque applied by pressing means in one direction selected from opening and closing directions of a control valve, and a motor torque applied by a DC motor in the opening or closing direction of the control valve, comprising: a PI controlled variable operation unit for receiving a deviation between input data indicative of a target opening/closing position of the control valve, and detection data indicative of a current opening/closing position of the control valve; a hysteresis correction unit for obtaining a hysteresis correction quantity from an output quantity of the PI controlled variable operation unit; and a motor driving voltage conversion unit for receiving a sum of the output quantity of the PI controlled variable operation unit and the hysteresis correction quantity, and converting the result into a voltage to be supplied to the DC motor.
Thus, by obtaining a hysteresis quantity from the output quantity of the PI controlled variable operation unit, and canceling the operation hysteresis of the control valve 11 based on the hysteresis correction quantity, it is possible to control the control valve with high accuracy and responsiveness.
The hysteresis correction unit may include: a changing direction determination unit composed of a differentiator for differentiating the output quantity of the PI controlled variable operation unit, and a code discriminator for determining whether an output of the differentiator is equal to 0 or lower; and a hysteresis correction quantity operation unit composed of an amplifier for amplifying an output of the code discriminator.
Thus, it is possible to obtain a proper hysteresis correction quantity with a simple constitution.
In accordance with the invention, there is provided a controller for an exhaust gas recirculation valve adapted to open/close on torque balance between a return torque applied by pressing means in one direction selected from opening and closing directions of a control valve, and a motor torque applied by a DC motor in the opening or closing direction of the control valve, comprising: a PI controlled variable operation unit for receiving a deviation between input data indicative of a target opening/closing position of the control valve, and detection data indicative of a current opening/closing position of the control valve; a hysteresis correction unit for obtaining a hysteresis correction quantity from an input quantity of the PI controlled variable operation unit; and a motor driving voltage conversion unit for receiving a sum an output quantity of the PI controlled variable operation unit and the hysteresis correction quantity, and converting the result into a voltage to be supplied to the DC motor.
Thus, by obtaining the hysteresis correction quantity of the control valve from the input quantity of the PI controlled variable operation unit, and canceling the operation hysteresis of the control valve based on the hysteresis correction quantity, it is possible to control the control valve with high accuracy and responsiveness.
The hysteresis correction unit may include: a positive/negative deviation determination unit for determining whether the input quantity of the PI controlled variable operation unit indicating a deviation between target and current values is equal to 0 or lower; and an amplifier for amplifying an output of the deviation positive/negative determination unit.
Thus, it is possible to obtain a proper hysteresis correction quantity with a simple constitution.